Determination of Solution Temperature in an Ex-Service Ni-Based Turbine Blade

It is well-known that the harsh operational conditions of turbine blades lead to a gradual change in the microstructure of underlying Ni-based superalloy of blades. Accordingly, a rejuvenation process should be conducted on turbine blades superalloys to recover their microstructures. The first and main step of the rejuvenation process is the determination of appropriate solution condition in which ϒʹ precipitates dissolve in the ϒ matrix. In this study, different heat treatment conditions were applied on a Ni-based single crystal superalloy to determine its solution condition. The results of scanning electron microscopy (SEM) showed that with increasing the solution treatment temperature from 1275°C (3h) to 1330°C (3h), at first, ϒʹ precipitates at dendritic regions dissolve and complete solution of ϒʹ phase occurs only after increasing the solution temperature to 1350°C (3h). The full solution condition (1350°C-3h) will be used as the first step of the rejuvenation process of these blades in future studies.